The Drag Force And Terminal Speed

The Drag Force And Terminal Speed

A fluid is anything that can flow-generally either a gas or a liquid. When there is a relative velocity between a body (either because the body moves through the fluid or because the fluid moves past the body), the body experiences a drag  force that opposes the relative motion and points in the direction in which the fluid flows relative to the body.

When a blunt body falls from rest through air, the drag force  is directed upward; its magnitude gradually increases from zero as the speed of the body increases.

where m is the mass of the body. As suggested in if the body falls long enough, D eventually equals  this means that a  and so the body’s speed no longer increases.

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However, if the cat does reach the acceleration vanishes and the cat relaxes somewhat, stretching its legs and neck horizontally outward and straightening its spine (it then resembles a flying squirrel).

6Th;s skier7rouches in an "egg "position" so as to minimize her effective cross-sectional area and thus the air drag acting on her.
6Th;s skier crouches in an egg
position  so as to minimize her effective
cross-sectional area and thus the
air drag acting on her.

The forces that act on a body falling through air: (a) the body when it has justbegun to fall and (b) the free-body diagram a little later, after a drag force has developed
The forces that act on a body falling through air: (a) the
body when it has just begun to fall and (b) the free-body diagram
a little later, after a drag force has developed.

"This is the distance through which the body must faU from rest to reach 95% of its terminal speed. Source: Adapted from Peter J. Brancazio, Sport Science, 1984, Simon & Schuster, New York.
This is the distance through which the body must  from rest to
reach 95% of its terminal speed.
Source: Adapted from Peter J. Brancazio, Sport Science, 1984, Simon
& Schuster, New York.

Humans often fall from great heights for the fun of skydiving. However, in
April 1987, during a jump, sky diver Gregory Robertson noticed that fellow sky diver Debbie Williams had been knocked Unconscious in a collision with a third sky diver and was unable to open her parachute. Robertson, who was well above Williams  at the time and who had not yet opened his parachute for the 4 km plunge.

A sky diver in a horizontal "spread eagle" maximizes the air drag.
A sky diver in a horizontal
spread eagle maximizes the air
drag.

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